membranes are composed of phospholipids and proteins= fluid mosaic model copyright © 2009 pearson...
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Membranes are composed of phospholipids and proteins= fluid mosaic model
Copyright © 2009 Pearson Education, Inc.
Phospholipidbilayer
Hydrophobic regionsof protein
Hydrophilicregions of protein
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Hydrophilichead
WATER
Hydrophobictail
WATER
Why Fluid?
- Many phospholipids are made from unsaturated fatty acids
– Cholesterol wedged into the bilayer keeps it liquid at lower temperatures
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Why mosaic?
◦ Proteins, enzymes, signaling molecules and transport proteins
Copyright © 2009 Pearson Education, Inc.Cholesterol
Glycoprotein
Glycolipid
Carbohydrate ofglycoprotein
Phospholipid
Microfilamentsof cytoskeleton
Integrin
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Transport proteins:
– Because membranes allow some substances to cross or be transported more easily than others, they exhibit selectively permeability
– Nonpolar molecules (carbon dioxide and oxygen) cross easily
– Polar molecules (glucose and other sugars) do not cross easily
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Diffusion is a process in which particles spread out evenly in an available space– No energy = passive
– Particles move from area of high concentration to low concentration until they reach equilibrium
– This means that particles diffuse down their concentration gradientMolecules of dye Membrane Equilibrium
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– Water moves across membranes in response to solute concentration inside and outside of the cell by a process called osmosis
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Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water
– Isotonic indicates that the concentration of a solute is the same on both sides
– Hypertonic indicates that the concentration of solute is higher outside the cell
– Hypotonic indicates a higher concentration of solute inside the cell
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Isotonic solution
(B) Lysed (C) Shriveled
(D) Flaccid (E) Turgid (F) Shriveled
Hypertonic solutionHypotonic solution
Plantcell
Animalcell
(A) Normal
Plasmamembrane
(plasmolyzed)
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Many substances do not freely diffuse across the membrane
– They require the help of specific transport proteins called aquaporins
– These proteins assist in facilitated diffusion, a type of passive transport that does not require energy
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Solutemolecule
Transportprotein
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Cells have a mechanism for moving a solute against its concentration gradient
– It requires the expenditure of energy in the form of ATP
– The mechanism alters the shape of the membrane protein through phosphorylation using ATP
Copyright © 2009 Pearson Education, Inc.
Transportprotein
Solute
Solute binding1 Phosphorylation2 Transport3
Proteinchanges shape
Protein reversion4
Phosphatedetaches
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Diffusion
Requires no energy
Passive transport
Higher solute concentration
Facilitateddiffusion
OsmosisHigher water
concentration
Higher soluteconcentration
Requires energy
Active transport
Solute
Water
Lower soluteconcentration
Lower waterconcentration
Lower soluteconcentration
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– Exocytosis is used to export bulky molecules, such as proteins or polysaccharides– What process did we learn about that ends with this?
– Endocytosis is used to import substances useful to the livelihood of the cell– Three different types:
1. Phagocytosis2. Pinocytosis3. Receptor-mediated endocytosis
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– Phagocytosis is engulfment of a particle by wrapping cell membrane around it, forming a vacuole
Phagocytosis
EXTRACELLULARFLUID
Pseudopodium
CYTOPLASM
Foodvacuole
“Food” orother particle
Foodbeingingested
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– Pinocytosis is the same thing except that fluids are taken into small vesicles
Pinocytosis
Plasmamembrane
Vesicle
Plasma membrane
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– Receptor-mediated endocytosis is where receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle
Coatedvesicle
Coatedpit
Specificmolecule
Receptor-mediated endocytosis
Coat proteinReceptor
Coatedpit
Material boundto receptor proteins
Plasma membrane